Packet transferring method, mobile communication system and mobile station

ABSTRACT

In a mobile Communication system which includes a base station controller, a plurality of radio base stations connected to the base station controller, and a mobile station simultaneously communicable with the plurality of radio base stations, the base station controller transfers a packet through the plurality of radio base stations to the mobile station. The mobile Station receives the packet as a plurality of reception packets through the plurality of radio base stations. The mobile station includes a controller that selects, among the plurality of reception packets supplied from the plurality of radio base stations, a best quality packet as a selected packet and sends, if the selected packet includes an error portion, a retransmission request to one of the plurality of base stations that sent the selected packet in order to request retransmission of a correct portion corresponding to the error portion.

This application claims priority to prior Japanese patent application JP2004-203162, the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

This invention relates to a mobile communication system including a basestation controller, a plurality of radio base stations connected to thebase station controller, and a mobile station simultaneouslycommunicable with the radio base stations and, in particular, to packetretransmission control from the mobile station to the radio basestations when a packet is transferred from the base station controllerthrough the radio base stations to the mobile station.

For example, a conventional mobile communication system is disclosed inJapanese Unexamined Patent Publication (JP-A) No. H 11-341541. Asillustrated in FIG. 1, the mobile communication system disclosed in thepublication comprises a base station controller 120 connected to acommunication network 110, a plurality of base stations 130-1 and 130-2connected to the base station controller 120, and a mobile station 140.The mobile station 140 transmits and receives packetized data throughradio channels to and from the base stations 130-1 and 130-2 each ofwhich is communicable with the mobile station 140.

In the above-mentioned mobile communication system, a packettransferring method disclosed in the above-mentioned publication is usedin case where the mobile station 140 transmits a transmission packet tothe base station controller 120 through each of the two base stations130-1 and 130-2. In this case, the base station controller 120 receivestwo transmission packets transferred through the two base stations 130-1and 130-2, respectively, and selects, as a selected packet, one of thetwo transmission packets which has a smaller number of transmissionerrors. The base station controller 120 transfers the selected packet tothe communication network 110.

However, the above-mentioned publication does not disclose packetretransmission for the purpose of reducing the transmission errors.

In particular, the above-mentioned publication does not disclose packetretransmission control from the mobile station to the radio basestations when a packet is transferred from the base station controllerthrough the radio base stations to the mobile station.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide packetretransmission control which is for use in a mobile communication systemincluding a base station controller, a plurality of radio base stations,and a mobile station simultaneously communicable with the radio basestations, and which is carried out from the mobile station to the radiobase stations when a packet is transferred from the base stationcontroller through the radio base stations to the mobile station,thereby achieving packet transfer with high reliability.

A packet transferring method according to this invention, a mobilecommunication system according to this invention, and a mobile stationaccording to this invention are as follows:

(1) A packet transferring method for use in a mobile communicationsystem including a base station controller, a plurality of radio basestations connected to the base station controller, and a mobile stationsimultaneously communicable with the plurality of radio base stations,the base station controller transferring a packet through the pluralityof radio base stations to the mobile station, the mobile stationreceiving the packet as a plurality of reception packets through theplurality of radio base stations, the mobile station carrying out thesteps of:

selecting, among the plurality of reception packets supplied from theplurality of radio base stations, a best-quality packet as a selectedpacket;

sending, if the selected packet includes an error portion, aretransmission request to one of the plurality of base stations in orderto request retransmission of a correct portion corresponding to theerror portion, the above-mentioned one of the plurality of base stationsbeing a sender of the selected packet; and

executing a data processing operation for the selected packet if theselected packet includes no error portion.

(2) The packet transferring method as described in the section (1),wherein the mobile station selects as the best-quality packet, if eachof the plurality of reception packets supplied from the plurality ofradio base stations includes the error portion, one of the plurality ofreception packets which requires retransmission of a smallest amount ofthe correct portion corresponding to the error portion.

(3) The packet transferring method as described in the section (1),wherein the mobile station selects as the best-quality packet, if eachof the plurality of reception packets supplied from the plurality ofradio base stations includes no error portion, one of the plurality ofreception packets which has been assembled from fragmented packets ofeach of the plurality of reception packets at an earliest time instantwithin a predetermined time period, the mobile station executes the dataprocessing operation for the selected packet selected as thebest-quality packet.

(4) The packet transferring method as described in the section (1),wherein the mobile station selects, as the best-quality packet, one ofthe plurality of reception packets from the radio base stations whichhas been received at an earliest time instant.

(5) A mobile communication system comprising a base station controller,a plurality of radio base stations connected to the base stationcontroller, and a mobile station simultaneously communicable with theplurality of radio base stations, the base station controllertransferring a packet through the plurality of radio base stations tothe mobile station, the mobile station receiving the packet as aplurality of reception packets through the plurality of radio basestations, wherein:

the mobile station comprises:

a processor; and

a controller for selecting, among the plurality of reception packetssupplied from the plurality of radio base stations, a best-qualitypacket as a selected packet,

for sending, if the selected packet includes an error portion, aretransmission request to one of the plurality of base stations in orderto request retransmission of a correct portion corresponding to theerror portion, the above-mentioned one of the plurality of base stationsbeing a sender of the selected packet, and

for making the processor execute a data processing operation for theselected packet if the selected packet includes no error portion.

(6) The mobile communication system as described in the section (5),wherein the controller in the mobile station selects as the best-qualitypacket, if each of the plurality of reception packets supplied from theplurality of radio base stations includes the error portion, one of theplurality of reception packets which requires retransmission of asmallest amount of the correct portion corresponding to the errorportion.

(7) The mobile communication system as described in the section (5),wherein the controller in the mobile station selects as the best-qualitypacket, if each of the plurality of reception packets supplied from theplurality of radio base stations includes no error portion, one of theplurality of reception packets which has been assembled from fragmentedpackets of each of the plurality of reception packets at an earliesttime instant within a predetermined time period, the mobile stationexecutes the data processing operation for the selected packet selectedas the best-quality packet.

(8) The mobile communication system as described in the section (5),wherein the controller in the mobile station selects, as thebest-quality packet, one of the plurality of reception packets from theradio base stations which has been received at an earliest time instant.

(9) A mobile station for use in a mobile communication system whichcomprises a base station controller, a plurality of radio base stationsconnected to the base station controller, and the mobile stationsimultaneously communicable with the plurality of radio base stations,the base station controller transferring a packet through the pluralityof radio base stations to the mobile station, the mobile stationreceiving the packet as a plurality of reception packets through theplurality of radio base stations, wherein:

the mobile station comprises:

a processor; and

a controller for selecting, among the plurality of reception packetssupplied from the plurality of radio base stations, a best-qualitypacket as a selected packet,

for sending, if the selected packet includes an error portion, aretransmission request to one of the plurality of base stations in orderto request retransmission of a correct portion corresponding to theerror portion, the above-mentioned one of the plurality of base stationsbeing a sender of the selected packet, and

for making the processor execute a data processing operation for theselected packet if the selected packet includes no error portion.

(10) The mobile station as described in the section (9), wherein thecontroller selects as the best-quality packet, if each of the pluralityof reception packets supplied from the plurality of radio base stationsincludes the error portion, one of the plurality of reception packetswhich requires retransmission of a smallest amount of the correctportion corresponding to the error portion.

(11) The mobile station as described in the section (9), wherein thecontroller selects as the best-quality packet, if each of the pluralityof reception packets supplied from the plurality of radio base stationsincludes no error portion, one of the plurality of reception packetswhich has been assembled from fragmented packets of each of theplurality of reception packets at an earliest time instant within apredetermined time period, the mobile station executes the dataprocessing operation for the selected packet selected as thebest-quality packet.

(12) The mobile station as described in the section (9), wherein thecontroller selects, as the best-quality packet, one of the plurality ofreception packets from the radio base stations which has been receivedat an earliest time instant.

In this invention, when a packet is transferred from the base stationcontroller via the radio base stations to the mobile station, the mobilestation receives a plurality of packets respectively from the radio basestations and selects, as a selected packet, one of the packets which hasa best quality. If the selected packet contains an error portion, themobile station requests retransmission of a correct portioncorresponding to the error portion to one of the radio base stationswhich is a sender of the selected packet. In this manner, it is possibleto achieve packet transfer with high reliability.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic block diagram of a conventional mobilecommunication system;

FIG. 2 is a block diagram of a mobile communication system according toan embodiment of this invention;

FIG. 3 is a view for describing packet fragmentation in the mobilecommunication system illustrated in FIG. 2;

FIG. 4 is a sequence chart for describing a flow of a downlink packet inthe mobile communication system illustrated in FIG. 2;

FIG. 5 is a sequence chart for describing a flow of an uplink packet inthe mobile communication system illustrated in FIG. 2;

FIG. 6 is a functional block diagram of a data packetdistributing/selecting portion illustrated in FIG. 2;

FIG. 7 is a functional block diagram of a data packet fragmentingassembling retransmission-control portion illustrated in FIG. 2; and

FIG. 8 is a flow chart for describing an operation of the data packet .fragmenting assembling retransmission-control portion illustrated inFIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Now, this invention will be described in detail with reference to thedrawing. Various operations for communication except those related tothis invention, including transmission and reception of a controlsignal, fragmenting and assembling of a packet, transmission andreception of the packet, are carried out by the use of known techniquesand detailed description thereof will be omitted.

At first referring to FIG. 2, a mobile communication system according toan embodiment of this invention will be described.

As illustrated in FIG. 2, the mobile communication system comprises abase station controller 20 connected to a packet node 10, two radio basestations 30-1 and 30-2, and a mobile station 40. The mobilecommunication system is substantially similar in structure to theconventional system described above but is different therefrom incharacteristic function. Although not shown in the figure, a greaternumber of radio base stations and a plurality of mobile stations areincluded in the mobile communication system.

The packet node 10 is a node in an upper communication network andserves to perform packet exchange or transfer. The packet node 10 isconnected to the base station controller 20 in the mobile communicationsystem. The packet node 10 transmits and receives packetized data(hereinafter will simply be referred to as a packet) to and from thebase station controller 20. Further, the packet node 10 transfers apacket to be transmitted to the base station controller 20 and a packetreceived from the base station controller 20 between the packet node 10and another packet node via the upper communication network. The basestation controller 20 is connected to the packet node 10 on one hand andto the radio base stations 30-1 and 30-2 on the other hand to transmitand receive a packet. The base station controller 20 communicates withthe mobile station 40 through the radio base stations 30-1 and 30-2 andradio channels and controls the radio base stations 30-1 and 30-2connected to the mobile station 40. For example, the mobile station 40is a mobile communication terminal including a mobile telephone andtransmits and receives a packet to and from the radio base stations 30-1and 30-2 using radio channels in a communicable region.

The base station controller 20 comprises data packettransmitting/receiving portions 21 and 22 and a data packetdistributing/selecting portion 23. Each of the data packettransmitting/receiving portions 21 and 22 is connected to the datapacket distributing/selecting portion 23.

The data packet transmitting/receiving portions 21 and 22 of the basestation controller 20 correspond to the radio base stations 30-1 and30-2 communicable with the mobile station 40, respectively, and aresupplied through the data packet distributing/selecting portion 23 witha downlink packet received from the packet node 10. The downlink packetthus supplied is sent from the data packet transmitting/receivingportion 21 to the radio base station 30-1 and from the data packettransmitting/receiving portion 22 to the radio base station 30-2.

Further, the data packet transmitting/receiving portion 21 receives anuplink packet from the radio base station 30-1. The data packettransmitting/receiving portion 22 receives an uplink packet from theradio base station 30-2. The data packet distributing/selecting portion23 has also a data packet combining function which receives and comparesthe uplink packets assembled in correspondence to the radio basestations 30-1 and 30-2, respectively. As a result of comparison, one ofthe uplink packets assembled and transferred first is selected andtransmitted to the packet node 10.

The radio base stations 30-1 and 30-2 have a same structure. Each of theradio base stations 30-1 and 30-2 comprises a data packettransmitting/receiving portion 31, a data packet fragmenting assemblingretransmission-control portion 32, an encoding/decoding portion 33, anda radio portion 34 which are connected in series in this order.

In the radio base station 30-1, the data packet transmitting/receivingportion 31 receives the downlink packet from the base station controller20 and sends the downlink packet to the data packet fragmentingassembling retransmission-control portion 32. Further, the data packettransmitting/receiving portion 31 transmits the uplink packet to thebase station controller 20. Depending upon a traffic condition at theradio base station 30-1 at that time instant, the data packetfragmenting assembling retransmission-control portion 32 has functionsof fragmenting the downlink packet into a plurality of blocks andcarrying out retransmission control with the mobile station 40. On theother hand, the data packet fragmenting assemblingretransmission-control portion 32 assembles fragmented packets from themobile station 40 into the uplink packet. The encoding/decoding portion33 encodes transmission data into encoded transmission data and decodesreception data. The radio portion 34 transmits the encoded transmissiondata as downlink fragmented packets to the mobile station 40 andreceives the transmission data from the mobile station 40 as uplinkfragmented packets. The radio base station 30-2 is operable in the samemanner and description thereof will be omitted.

The mobile station comprises a first receiver 41 corresponding to theradio base station 30-1, a first decoder 42 connected to the firstreceiver 41, a second receiver 43 corresponding to the radio basestation 30-2, a second decoder 44 connected to the second receiver 43, adata packet fragmenting assembling retransmission-control portion 45corresponding to both of the radio base stations 30-1 and 30-2, a datapacket processor 46 connected to the data packet fragmenting assemblingretransmission-control portion 45, an encoder 47, and a transmitter 48connected to the encoder 47. Each of the first and the second decoders42 and 44 and the encoder 47 is connected to the data packet fragmentingassembling retransmission-control portion 45.

The first and the second receivers 41 and 43 receive the downlinkfragmented packets from the radio base stations 30-1 and 30-2,respectively. The first and the second decoders 42 and 44 decode thedownlink fragmented packets. The data packet fragmenting assemblingretransmission-control portion 45 selects one of the radio base stations30-1 and 30-2 which is a sender of the downlink fragmented packetshaving a smaller number of errors or the downlink fragmented packetsreceived earlier by a predetermined time. The data packet fragmentingassembling retransmission-control portion 45 has a retransmissioncontrol function and assembles a plurality of downlink fragmentedpackets into a single downlink packet. The data packet fragmentingassembling retransmission-control portion 45 fragments the uplink packetinto a plurality of uplink fragmented packets and sends the uplinkfragmented packets to the encoder 47. In case where retransmissioncontrol is carried out, a retransmission request including radio basestation information and retransmission control information is sent tothe encoder 47. The data packet processor 46 carries out data processingfor the packets and produces the uplink packet from the transmissiondata. The encoder 47 encodes the transmission data into the encodedtransmission data. The transmitter 48 transmits the encoded transmissiondata as the uplink fragmented packets to the radio base stations 30-1and 30-2.

Referring to FIG. 3 in addition to FIG. 2, a data processing operationrelated to fragmenting of a downlink data packet will be described as acharacteristic of this invention. The data packet is fragmenteddepending upon the traffic condition of each of the radio base stations30-1 and 30-2.

In the illustrated example, the base station controller 20 sends adownlink data packet having a length of 1 kbyte to each of the radiobase stations 30-1 and 30-2.

Depending upon the traffic condition of each of the radio base stations30-1 and 30-2, the data packet fragmenting assemblingretransmission-control portion 32 fragments the data packet into aplurality of data blocks. Specifically, in the radio base station 30-1,the data packet fragmenting assembling retransmission-control portion 32fragments the data packet having a length of 1 kbyte into 10 packetseach having a length of 100 bytes. In the radio base station 30-2, thedata packet fragmenting assembling retransmission-control portion 32fragments the data packet having a length of 1 kbyte into 5 packets eachhaving a length of 200 bytes. The radio base stations 30-1 and 30-2independently send the data blocks to the mobile station 40 connectedthereto. The mobile station 40 is connected to both of the radio basestations 30-1 and 30-2 and receives, as reception data packets, the datablocks from the radio base stations 30-1 and 30-2 by the data packetfragmenting assembling retransmission-control portion 45.

Consideration will be made about the case where the data packetfragmenting assembling retransmission-control portion 45 detects atransmission error in a data block #1 in each of the two reception datapackets. The number of bytes of the data block #1 supplied from theradio base station 30-1 is equal to a half of the number of bytes of thedata block #1 supplied from the radio base station 30-2. Therefore, thedata packet fragmenting assembling retransmission-control portion 45selects the radio base station 30-1 which is a sender of the data block#1 having a smaller packet length. In case where a plurality of datablocks contain errors (those data blocks containing errors may also becalled error data blocks or error portions), the data packet fragmentingassembling retransmission-control portion 45 selects, for example, theradio base station 30-1 which is a sender of the error data blocks witha smaller total number of errors. The data packet fragmenting assemblingretransmission-control portion 32 of the radio base station 30-1 issupplied with a retransmission request for the error data block orblocks (error portion or portions). The data packet fragmentingassembling retransmission-control portion 32 of the radio base station30-2 which is not supplied with a retransmission request discards atransmission data packet which has been retained for retransmission.

In other words, when the base station controller 20 transfers a packetto the mobile station 40 via the radio base stations 30-1 and 30-2, thedata packet fragmenting assembling retransmission-control portion 45 ofthe mobile station 40 selects, as a selected packet, one of receptionpackets from the radio base stations 30-1 and 30-2 which has a bestquality (best-quality packet). If the selected packet contains an errorportion, the data packet fragmenting assembling retransmission-controlportion 45 sends a retransmission request for the error portion to oneof the radio base stations 30-1 and 30-2 which is a sender of theselected packet. If the selected packet contains no error portion, theselected packet is subjected to data processing at the data packetprocessor 46.

Preferably, in case where both of the reception packets from the radiobase stations 30-1 and 30-2 contain error portions, the data packetfragmenting assembling retransmission-control portion 45 of the mobilestation 40 selects, as the best-quality packet, one of the receptionpackets which requires a smaller amount of retransmission of the errorportion.

In case where both of the reception packets from the radio base stations30-1 and 30-2 do not contain error portions, the data packet fragmentingassembling retransmission-control portion 45 of the mobile station 40selects, as the best-quality packet, one of the reception packets whichhas been assembled from the fragmented packets first (or, at an earliesttime instant) within a predetermined time period. The selected packet isprocessed by the data packet processor 46.

The data packet fragmenting assembling retransmission-control portion 45of the mobile station 40 may select, as the best-quality packet, one ofthe reception packets from the radio base stations 30-1 and 30-2 whichhas been received first.

Next referring to FIG. 4 in addition to FIG. 2, description will be madeof transfer of the downlink packet in the mobile communication system.

In the base station controller 20, the data packetdistributing/selecting portion 23 distributes the downlink packetsupplied from the packet node 10 to each of the data packettransmitting/receiving portions 21 and 22 corresponding to the radiobase stations 30-1 and 30-2 communicable with the mobile station 40 inaccordance with a destination address contained in the packet. Thepacket thus distributed is transmitted from the data packettransmitting/receiving portion 21 to the radio base station 30-1 on onehand and from the data packet transmitting/receiving portion 22 to theradio base station 30-2 on the other hand (step S1).

The downlink packet supplied from the base station controller 20 to theradio base station 30-1 is sent from the data packettransmitting/receiving portion 31 to the data packet fragmentingassembling retransmission-control portion 32. The data packetfragmenting assembling retransmission-control portion 32 fragments thereception packet into a plurality of blocks as fragmented transmissionpackets and temporarily retains the fragmented transmission packets forretransmission control between the radio base station 30-1 and themobile station 40 as a retransmission preparation step (step S3). On theother hand, the transmission data are encoded by the encoding/decodingportion 33 into the encoded transmission data. The encoded transmissiondata are transmitted from the radio portion 34 to the mobile station 40as the downlink fragmented packets. The radio base station 30-2 isoperable in the similar manner.

In the mobile station 40, the first receiver 41 receives the downlinkfragmented packets from the radio base station 30-1 as receptionpackets. The second receiver 43 receives the downlink fragmented packetsfrom the radio base station 30-2 as reception packets. The receptionpackets are decoded by the first and the second decoders 42 and 44 intoreception data, respectively. The data packet fragmenting assemblingretransmission-control portion 45 compares the two reception data andselects, for example, one of the radio base stations 30-1 and 30-2 whichis a sender of the reception packets containing an error fragmentedpacket having a shorter error packet length (step S4). Specifically, ifthere is a plurality of error fragmented packets, one of the radio basestations 30-1 and 30-2 which is a sender of the reception packetscontaining the error fragmented packets with a shorter total length isselected. If the transmission error is detected in the receptionpackets, the selected radio base station, for example, the radio basestation 30-1 is supplied with a retransmission request through theencoder 47 and the transmitter 48 (step S5).

In the radio base station 30-1, the data packet fragmenting assemblingretransmission-control portion 32 receives the retransmission requestvia the radio portion 34 and the encoding/decoding portion 33. Among thetransmission packets temporarily retained, a designated downlinkfragmented packet is retransmitted to the mobile station 40 as adestination (step S6).

If the mobile station 40 receives the downlink fragmented packetnormally, i.e., without an error, the downlink fragmented packet issubjected to data processing at the data packet processor 46 (step S7).The radio base station 30-2 which is not supplied with theretransmission request cancels retransmission preparation and discardsthe transmission packets temporarily retained.

Next referring to FIG. 5 in addition to FIG. 2, description will be madeof transfer of the uplink packet in the mobile communication system.

The data packet processor 46 of the mobile station 40 produces theuplink packet from the transmission data. The uplink packet thusproduced is sent to the data packet fragmenting assemblingretransmission-control portion 45 and fragmented into the uplinkfragmented packets. The uplink fragmented packets are sent to theencoder 47 to be encoded into encoded uplink fragmented packets. Thetransmitter 48 transmits the encoded uplink fragmented packets to theradio base stations 30-1 and 30-2 (step S11).

The data packet fragmenting assembling retransmission-control portion 45makes retransmission preparation in case of reception of theretransmission request (step S12).

For example, in the radio base station 30-2, the radio portion 34receives the uplink fragmented packets from the mobile station 40 andsends the uplink fragmented packets to the encoding/decoding portion 33.The encoding/decoding portion 33 decodes the uplink fragmented packetsinto decoded uplink fragmented packets and transfers the decoded uplinkfragmented packets to the data packet fragmenting assemblingretransmission-control portion 32. If a transmission error in anyfragmented packet or packets is detected, the data packet fragmentingassembling retransmission-control portion 32 sends a retransmissionrequest for an error fragmented packet or packets as the error portionor portions to the mobile station 40 through the encoding/decodingportion 33 and the radio portion 34 (step S13). The retransmissionrequest contains radio base station information and retransmissioncontrol information.

When the mobile station 40 is supplied with the retransmission requestfrom the radio base station 30-2, the data packet fragmenting assemblingretransmission-control portion 45 receives the retransmission requestvia the second receiver 43 and the second decoding portion 44. Among thetransmission packets temporarily retained, a designated uplinkfragmented packet is retransmitted to the radio base station 30-2 as adestination (step S14). The data packet fragmenting assemblingretransmission-control portion 45 makes retransmission preparation incase of reception of the retransmission request (step S15).

The fragmented packets retransmitted to the radio base station 30-2 arereceived by the radio portion 34 and sent to the encoding/decodingportion 33. The retransmitted fragmented packets are decoded by theencoding/decoding portion 33 and transferred to the data packetfragmenting assembling retransmission-control portion 32. The datapacket fragmenting assembling retransmission-control portion 32assembles normal fragmented packets, including the retransmittedfragmented packets, into the uplink packet. The uplink packet thusassembled is transmitted from the data packet transmitting/receivingportion 31 to the base station controller 20 (step S16).

On the other hand, in the radio base station 30-1, the uplink fragmentedpackets from the mobile station 40 are transferred via the radio portion34 and the encoding/decoding portion 33 to the data packet fragmentingassembling retransmission-control portion 32. The data packetfragmenting assembling retransmission-control portion 32 assemblesnormal fragmented packets into the uplink packet. The uplink packet istransmitted from the data packet transmitting/receiving portion 31 tothe base station controller 20 (step S21).

In the base station controller 20, the data packettransmitting/receiving portion 21 receives the uplink packet from theradio base station 30-1 and the data packet transmitting/receivingportion 22 receives the uplink packet from the radio base station 30-2.These uplink packets are sent to the data packet distributing/selectingportion 23. The data packet distributing/selecting portion 23 comparesthe two uplink packets respectively assembled and transmitted incorrespondence to the radio base stations 30-1 and 30-2 and selects, asa selected packet, one of the uplink packets which has first beenassembled and transmitted. The selected packet is transmitted to thepacket node 10 (step S21).

In the illustrated example, the uplink packet from the radio basestation 30-1 without the retransmission control is selected while theuplink packet from the radio base station 30-2 is discarded.

Next referring to FIG. 6, description will be made of the data packetdistributing/selecting portion 23 of the base station controller 20.

The data packet distributing/selecting portion 23 comprises a datapacket receiving unit 51, a data packet distributing unit 52, afirst-assembled packet selecting unit 53, and a data packet deliveringunit 54.

The data packet receiving unit 51 sends the downlink packet receivedfrom the packet node 10 to the data packet distributing unit 52. Thedata packet distributing unit 52 distributes the downlink packetsupplied thereto to the radio base stations 30-1 and 30-2. When theuplink packets from the same sender are supplied from the radio basestations 30-1 and 30-2, the first-assembled packet selecting unit 53selects, as a selected uplink packet, one of the uplink packets whichhas first been assembled, and sends the selected uplink packet to thedata packet delivering unit 54. The data packet delivering unit 54delivers the selected uplink packet supplied thereto to the packet node10.

In the foregoing description, in retransmission control of the downlinkpacket, the mobile station 40 selects the radio base station which is asender of the error packet or packets with a shortest error packetlength. Alternatively, the radio base station which is a sender of thepacket received earlier by a predetermined time may be selected. In theforegoing description, the packet is distributed to the two radio basestations. However, the packet may be distributed to a greater number ofthe radio base stations.

As described above, a best-quality channel is selected from a pluralityof radio channels so that the reliability of communication is improved.In addition, by the use of the radio channel selecting technique capableof reducing a packet transfer time in retransmission control, it ispossible to improve the efficiency of communication.

Referring to FIG. 7, description will be made of the data packetfragmenting assembling retransmission-control portion 45 of the mobilestation 40.

The data packet fragmenting assembling retransmission-control portion 45comprises a transmission data packetizing unit 61, an uplink fragmentedpacket transmitting unit 62, a downlink fragmented packet receiving unit63, a downlink fragmented packet assembling transmitting unit 64, anerror packet comparing selecting unit 65, an error packet retransmissionrequesting unit 66, and a single packet detecting timer (hereinaftersimply be referred to as a timer) 67.

The transmission data packetizing unit 61 is connected to the uplinkfragmented packet transmitting unit 62 and packetizes transmission datainto uplink fragmented packets which are sent to the uplink fragmentedpacket transmitting unit 62. The uplink fragmented packet transmittingunit 62 is connected to the error packet retransmission requesting unit66 and the encoder 47 and transmits the uplink fragmented packetssupplied from the transmission data packetizing unit 61 or theretransmission request supplied from the error packet retransmissionrequesting unit 66 to the encoder 47.

The downlink fragmented packet receiving unit 63 is connected to thedownlink fragmented packet assembling transmitting unit 64. The downlinkfragmented packet receiving unit 63 receives the downlink fragmentedpackets from the radio base stations 30-1 and 30-2 through the first andthe second decoders 42 and 44, respectively, and transfers the downlinkfragmented packets to the downlink fragmented packet assemblingtransmitting unit 64. The downlink fragmented packet assemblingtransmitting unit 64 is connected to the error packet comparingselecting unit 65 and the data packet processor 46. The downlinkfragmented packet assembling transmitting unit 64 transfers the errorpacket to the error packet comparing selecting unit 65 and assembles thedownlink fragmented packets supplied thereto into a normal packet totransmit the normal packet to the data packet processor 46. When thenormal packet is delivered, other packets from the same sender arediscarded.

The error packet comparing selecting unit 65 is connected to the errorpacket retransmission requesting unit 66 and the timer 67. The errorpacket comparing selecting unit 65 is supplied with the error packetfrom the downlink fragmented packet assembling transmitting unit 64 andstarts the timer 67. When another packet from the same sender isdetected, the timer 67 is initialized and these packets are comparedunder a predetermined condition to select one of these packets. When atimer period of the timer 67 has lapsed, it is judged that anindependent packet from only one radio base station is received.Therefore, upon completion of assembling of the fragmented packets, theerror packet comparing selecting unit 65 transmits the retransmissionrequest through the error packet retransmission requesting unit 66 inorder to request retransmission of the error packet. As thepredetermined condition, the error packet comparing selecting unit 65supplied with a plurality of packets compares the total numbers of bytesof the error packets and selects the radio base station which is asender of the error packet requiring retransmission of a shortest totalpacket length. The error packet comparing selecting unit 65 sends anotice indicating the result of selection to the error packetretransmission requesting unit 66. The notice includes radio basestation information and retransmission control information.

In response to the notice from the error packet comparing selecting unit65, the error packet retransmission requesting unit 66 transmits theretransmission request to the encoder 47 through the uplink fragmentedpacket transmitting unit 62.

Next referring to FIG. 8 in addition to FIG. 7, description will be madeof an operation of receiving the downlink fragmented packets. At first,the timer 67 is initialized when a power supply is turned on (step S71).

Supplied with the fragmented packets decoded by the first or the seconddecoder 42 or 44 through the downlink fragmented packet receiving unit63, the downlink fragmented packet assembling transmitting unit 64assembles the fragmented packets (step S72). At this time, the errorpacket is transferred to the error packet comparing selecting unit 65.

It is assumed that no error packet is detected (NO in step S73). In thisevent, upon completion of assembling of the downlink fragmented packetsinto the downlink packet (step S74), the downlink fragmented packetassembling transmitting unit 64 transmits the downlink packet thusassembled to the data packet processor 46 (step S75). Then, theoperation comes to an end.

In presence of the error packet (YES in step S73), the downlinkfragmented packet assembling transmitting unit 64 sends the errorfragmented packet to the error packet comparing selecting unit 65. Theerror packet comparing selecting unit 65 starts the timer 67 (step S81)to start time monitoring and checks presence or absence of the errorfragmented packet supplied from another radio base station to the mobilestation 40 as the same destination (step S82).

If the error fragmented packet addressed to the same destination isreceived (YES in step S83), the error packet comparing selecting unit 65initializes the timer 67 (step S84). On the other hand, the error packetcomparing selecting unit 65 calculates the error packet length for eachof the two reception packets and compares the error packet lengths,i.e., the byte lengths to be retransmitted (step S85). In case of thepackets received from a plurality of radio base stations, one of theradio base stations which is a sender of the packet having a shortestpacket length is selected as a result of comparison (step S86). Theerror packet comparing selecting unit 65 transfers the radio basestation information indicative of the selected radio base station andthe error packet subjected to retransmission to the error packetretransmission requesting unit 66. The error packet retransmissionrequesting unit 66 processes the retransmitted data into fragmentedpackets and sends the retransmission request for the error packet to theselected radio base station (step S87). Then, the operation returns tothe step S72 to wait reception of a retransmitted packet correspondingto the error packet.

If the same packet is not received (NO in step S83) and the timer periodof the timer 67 has lapsed (YES in step S88), the timer 67 isinitialized (step S89). Then, the operation proceeds to the step S87.Specifically, the error packet comparing selecting unit 65 transfers theradio base station information indicative of the selected radio basestation and the error packet subjected to retransmission to the errorpacket retransmission requesting unit 66. The error packetretransmission requesting unit 66 processes the retransmitted data intothe fragmented packets and sends the retransmission request for theerror packet to the selected radio base station.

While the present invention has thus far been described in connectionwith the preferred embodiment thereof, it will readily be possible forthose skilled in the art to put this invention into practice in variousother manners.

The invention claimed is:
 1. A wireless communication system comprising:plural base stations; and a mobile station, wherein said mobile stationis connected to each of said plural base stations, said mobile stationselects a best-quality packet among packets that derive from a packet,the packets being transmitted from said plural base stations, saidmobile station selects a part of said plural base stations based on saidbest-quality packet, and said mobile station requests retransmission tosaid part of said plural base stations when said mobile station does notreceive said packets correctly.
 2. The wireless communication systemaccording to claim 1, wherein said packets include same data which istransmitted from an upper node.
 3. The wireless communication systemaccording to claim 1, wherein said part of said plural base stations isone base station.
 4. The wireless communication system according toclaim 1, wherein said best-quality packet is selected based on one ofsmallest packet size among said packets.
 5. A mobile station comprising:selecting unit configured to select a best-quality packet among packetsthat derive from a packet, the packets being transmitted from pluralbase stations, and select a part of said plural base stations based onsaid best-quality packet; and requesting unit configured to requestretransmission to said part of said plural base stations when saidmobile station does not receive said packets correctly, wherein saidmobile station is connected to each of said plural base stations.
 6. Themobile station according to claim 5, wherein said packets include samedata which is transmitted from an upper node.
 7. The mobile stationaccording to claim 5, wherein said part of said plural base stations isone base station.
 8. The mobile station according to claim 5, whereinsaid best-quality packet is selected based on one of smallest packetsize among said packets.
 9. A communication control method in a mobilestation comprising: selecting a best-quality packet among packets thatderive from a packet, the packets being transmitted from plural basestations; selecting a part of said plural base stations based on saidbest-quality packet; and requesting retransmission to said part of saidplural base stations when said mobile station does not receive saidpackets correctly, wherein said mobile station is connected to each ofsaid plural base stations.
 10. The mobile station according to claim 9,wherein said packets include same data which is transmitted from anupper node.
 11. The mobile station according to claim 9, wherein saidpart of said plural base stations is one base station.
 12. The mobilestation according to claim 9, wherein said best-quality packet isselected based on one of smallest packet size among said packets.